Seeing ourselves in our mind, doing the thing we fear, is one of the most important tips for improving self confidence, in situations where we feel we lack it. It has to happen in mind before it can happen in reality.
We need to be comfortable with the mental scene, before we can take the first step towards acting it out. If we are able to picture ourselves in our mind - doing the thing we fear, and being comfortable and natural doing it - then its half the battle won.
That mental picture needs to be repeated often, to reinforce the feeling of confidence and assurance in doing what we fear. Once it feels easy enough in the mind, it is time to act it out.
For instance, let's say it is presentation time at work, and public speaking is not exactly your forte. Let us assume you are prepared with the actual material, and it is just the stage jitters that is doing you.
A few days before the presentation, practice doing the perfect presentation in your mind. See yourself doing it naturally, without any trace of fear or doubt, and looking your best and being confident when speaking on the stage.
Imagine the audience enraptured while taking in what you have to say. You can even imagine cracking a joke during the presentation, and the audience responding with a laugh. Heck.. it's your world in your mind, you can pretty much imagine whatever, so long it gives you the right kick!
Keep doing it everyday, even multiple times a day, until you are comfortable with the idea, and making that presentation feels natural to you. That kind of mental preparation is what goes a long way in making for the successful presentation, when the time comes for you to act out your thoughts in reality.